Parkinson’s disease is experiencing an ever-increasing prevalence, the fastest in the world for this type of disease, and which remains unexplained by currently identified factors. This increase in the number of people affected is becoming a major concern for public health authorities around the world. Researchers recently found that the common and widely used chemical trichlorethylene (TCE) is associated with a 500 percent increased risk of developing the disease. Once used to de-caffeine coffee, degrease metal, and dry-clean clothes, it is a long-lasting pollutant.
The number of people with Parkinson’s disease has more than doubled in the last thirty years and, barring significant changes, will double again by 2040. Many genetic causes or risk factors for the disease have been identified, but the vast majority of people do not carry any of these mutations. Some toxic substances, especially some pesticides, are also associated with the disease.
However, these elements are not enough to explain the alarming increase in the number of cases, as well as the aging of the population itself. Other less obvious reasons should contribute to its growth. One of these could be trichlorethylene (TCE), a ubiquitous chemical that contaminates countless objects and poses a health hazard to those who are exposed to it, whether in their work environment or in the environment.
In a hypothesis paper published in the Journal of Parkinson’s Disease, an international team of researchers at the University of Rochester Medical Center (URMC) suggests that TCE may be an invisible agent in Parkinson’s disease. The researchers detail the chemical’s widespread use and present evidence for the toxicant’s association with Parkinson’s through profiles of seven people who developed the disease.
A ubiquitous industrial pollutant that causes various diseases.
TCE is a solvent that has long been widely used in a variety of industrial, civil, military, and medical applications, including paint removal, typing, engine cleaning, and patient anesthesia. Its use in the United States reached its peak in the 1970s.
Although home use has since declined, TCE is still used for metal degreasing and dry cleaning. A closely related chemical, perchlorethylene (PCE), largely replaced TCE in dry cleaning in the 1950s. However, under anaerobic conditions, PChE is often converted to TCE and their toxicity is similar.
The link between TVE and Parkinson’s disease was first hinted at in case studies over 50 years ago. Since then, studies in mice and rats have shown that TCE readily penetrates brain and body tissues and, at high doses, damages the energy-producing parts of cells, the mitochondria. In animal studies, TCE causes a selective loss of dopamine-producing nerve cells, a hallmark of Parkinson’s disease in humans.
Invisible pollution and growing risk
Of course, people who have directly worked with TCE have a high risk of developing Parkinson’s disease. However, the authors warn in their statement that “millions of people are unknowingly exposed to this chemical through outdoor air, contaminated groundwater, and indoor air pollution.”
This is because the chemical can contaminate soil and groundwater, spreading pollution long distances and migrating over time. In addition to water hazards, volatile fuels can easily evaporate and enter buildings (homes, schools and workplaces) undetected.
Illustration of pollution associated with TCEs. © Dorsey, E. Ray et al. 2023
The detection of TCE fumes was first reported in the 1980s when radon was found to evaporate from the ground and enter homes, increasing the risk of lung cancer. Today, millions of homes are tested for radon, but only a few are tested for TCEs.
public health issue
The authors note that “for more than a century, TCEs have threatened workers, polluted the air we breathe, both indoors and outdoors, and polluted the water we drink. Not to mention that global usage is on the rise.”
Although the European Union and two US states have banned TCEs, they are still allowed for certain industrial uses in Europe. Globally, TCE consumption is expected to increase by 3% per annum, with China, the fastest growing country, currently accounting for half of the global market.
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The authors propose a number of actions to combat the threat. In particular, they note that contaminated sites can be successfully remediated and indoor air exposure can be reduced with vapor treatment systems similar to those used for radon.
In addition, they advocate for more research to better understand how TCEs contribute to Parkinson’s and other diseases. TCE levels in groundwater, drinking water, soil, ambient air and indoor air require more careful monitoring and this information should be brought to the attention of those who live and work near contaminated sites as a matter of priority.
Finally, the authors call for a permanent end to the use of these chemicals in the United States as well as around the world. PCE is still widely used in dry cleaning and TCE in steam degreasing. Of course, it will be difficult to recognize this chemical as a risk factor, since decades pass between exposure to TVE and the onset of symptoms of Parkinson’s disease.